For at least the last 100 years, it has been known to provide clocks with a movable moon display which feature shows a replica of the moon passing from one side of a display opening in the clock face to the other in timed relation with the timekeeping mechanism of the clock. Early versions of such moon displays are disclosed in U.S. Pat. No. 508,467, granted Nov. 14, 1893, U.S. Pat. No. Des. 23,026, granted Jan. 30, 1894 and U.S. Pat. No. 1,126,214 granted Jan. 26, 1915. In the usual moon display, the clock face is provided with an arcuate display opening, generally shaped as a semicircular segment for simplicity, and arranged behind this opening is a moon dial or disc of a size, e.g., diameter, large enough to completely fill the opening. On the front face of the dial is at least one replica of the moon and commonly a second replica is included at a diametrically opposite location on the dial face. Each moon replica is of a diameter considerably smaller than the radius of the display opening to be visible in full therethrough. The moon dial is rotated about its axis in periodic small stepwise increments, usually by means of a ratchet and pawl drive although other drives can be substituted. The ratchet teeth are conveniently formed around the outside periphery of the dial, beyond the limits of the display opening so as to be hidden from view, and are engaged by a pawl rocked periodically by gears or the like driven from the mechanical works of the clock. Thus, gradual rotation of the dial causes the moon replica to advance slowly across the display opening in a roughly 180.degree. arc, simulating the changes in the moon during the lunar cycle. Through appropriate selection of gear ratios, this simulated moon behavior can be generally coordinated timewise with the changes of the real moon. If desired, the margins of the clock face on each side (or ends in terms of moon replica travel) of the display opening can be formed as a protruding semicircular extension corresponding in radius to the moon replica so as to overlap with the replica regressively, i.e., from new moon to full moon, as the replica enters the display opening and then progressively as it leaves the opening and thus more closely resemble the changing appearances of the moon during the lunar cycle.
Movable moon displays of this type are commonly seen in large case clocks, such as tall case or grandfather's clocks but they are also found in smaller clocks such as wall clocks or mantle clocks and have even been adapted for wristwatches and the like. Most often, the moon display is situated at the top end of the clock face above the dial, as can be seen in U.S. Pat. No. 1,126,214, identified above, but it can also be situated within the hour dial as appears in U.S. Pat. No. 508,467. The moon replica itself can take the form of a plain circular area of a light color, e.g., yellow or golden, associated with the moon but custom apparently favors the inclusion of human facial characteristics no doubt symbolic at least in caricature of the proverbial "man in the moon." However, the moon replica can show more accurate astronomical features as seen in U.S. Pat. Des. No. 244,672. The remainder of the front face of the moon dial is of a contrasting coloration, normally dark in tone to represent the night sky and ornamentation suggestive of stars and other cosmic objects, either real or figurative, is commonly added.
In standard moon displays known in the art, the moon dial or disc is a continuous circular plate with flat front and rear faces carrying on its front face the indicia referred to above applied thereto by paint, enamel, metallic embellishment or the like. Consequently, the visual appearance of the moon replica necessarily gives a crude prosaic one-dimensional impression which remains fixed during the passage of the replica, across the display. Such moon displays unfortunately lack even a hint of realism or any change in effect that might add interest to their visual impression.
In recent years, with a focus on increased sophistication, moon displays have been designed to convey a more controlled simulation of the change in the phases of the moon, as can be found in U.S. Pat. Nos. 4,548,512, granted Oct. 22, 1985, 4,684,260, granted Aug. 4, 1987 and 4,692,031, granted Sep. 8, 1987. In these more complex devices, the moon dial and moon replica are made separate, the moon dial having one or more small circular moon openings therein corresponding to the size of the moon replica. A second small disc of less than one-half the dial diameter is situated behind each such moon opening and the face of this disc is colored to simulate the moon's appearance except for one or more dark circular regions generally coextensive in diameter with the moon opening in the dial. The separate moon dial and replica disc are mounted for independent relative rotation, with the replica disc translating bodily with the dial as the latter rotates while being itself rotated independently in gradual steps about its own axis. In this manner, changes in the phase of the moon replica can be achieved independently of the movement of the dial as a whole by rotating the dark replica region into and out of view through the moon opening, the remaining light colored replica region seen through the moon openings representing the waning and then waxing moon. In this way, the relative positions of the opening and the replica are precisely adjustable and the replica can remain in a given phase position as the moon dial as a whole makes a daily transit through the display opening in the clock face, the phase relation being gradually changed during subsequent transits.
Nevertheless, even in these more sophisticated constructions, any suggestion of depth or suspension in space for the moon replica is minimal and is only incidental to the need for independent relative rotation of the dial and replica disc, necessitating two separate elements, rather than being deliberately emphasized. The axial separation between the elements is slight at best and the area of the replica disc has to greatly exceed that of the associated moon opening in the dial so that the dial opening is essentially completely blocked by the closely proximate replica disc. Hence, even if illumination were present within the clock interior, it would not be visible through the moon opening.